Niantic keeps their release rarity housed on their own servers, we cannot say exactly how rare Special Items really are. Suffice to say they’re incredibly difficult to find, and we should not take their usage lightly. Keep them secret, keep them safe!

@krakmh you can get all of these special evolution items by spinning PokeStops. And all of these items are going to drop randomly and there is absolutely no way to find the pattern as they are ultra-rare.

As pointed out by @Zaidi_Bai, you need to play harder. Persistence is the key here. So keep spinning those PokeStops as much as you possibly can.